In a reversing stand, the stock is reduced in thickness in a back and forth motion in a sequence of passes. In the case of known cold-rolling mills, an oil/water emulsion having an oil concentration of around 0.5 to 5% is normally used for roll gap lubrication, roll cooling and roll cleaning. If the oil concentration is increased, the lubricating effect generally increases, i.e. there is less roll gap friction, whereas the cooling effect is reduced.
In the case of tandem mills, approximately ⅓ the quantity of emulsion per stand is applied to the work rolls or to the metal strip on the entry side immediately upstream of the roll gap for roll gap lubrication. The remaining ⅔ are used on the exit side primarily for cooling the work rolls but also for roll cleaning, particularly for cleaning the back-up rolls.
In the case of a reversing stand, all the emulsion for each roll is generally applied on the entry side to the work rolls or to the strip immediately upstream of the roll gap.
Depending on the installed power of the main drives, the flow rate for a cold-rolling mill is e.g. 0.8 l per minute and kilowatt hour of input power. For a input power of 6000 kW per stand, for example, this means a coolant/lubricant (emulsion) flow rate of 4800 l per minute.
Despite this large quantity of lubricant, the required amount of lubricant in the roll gap may be inadequately adjusted. In particular, the problem arises that the amount of oil available in the roll gap for roll gap lubrication is primarily predetermined by the cooling requirements and not by the current lubrication requirements in the roll gap. It must be assumed that, in the case of emulsion lubrication in the roll gap, the oil concentration will be well below 100%, resulting in a reduced lubricating action. In practice, this means that the rolling oil consumption is much higher than the amount of lubricant actually required for lubricating the roll gap. Selectively controlling the current lubrication and friction conditions is only possible to a limited extent in this manner, e.g. only via the oil concentration in the emulsion or via additives.
In WO 2005/115651 A1 it is therefore proposed to inject a base oil without water as a carrier medium into the roll gap. As the lubricant is applied to the stock before it enters the roll gap, an appropriate quantity of lubricant for an even application is necessary.